E.B.
I grew up going to camp every summer when I was growing up. Eventually I worked as a counselor at that same camp.
One of the problems that I encountered most often was kids not knowing what was in their own suitcase or backpack or trunk. Many times I heard things like "my mom packed this but I'm not sure what it is" or "I don't know if my mom packed my sneakers" or "I'm not sure if my dad wanted me to use this towel for showers or for swimming" or "can you help me turn this [flashlight/lantern/alarm clock] on? My dad bought it for me to use here but I don't know how it works" or "hey, I didn't know this whole time that I had sunscreen in my bag". One summer when I was a counselor, a girl had her very first period. Her mom had thrown a bunch of tampons and pads into the girl's suitcase, but the girl had never been taught how to use them - the girl didn't even realize the supplies were there. Apparently the mom just threw them in last minute. The camp nurse had to step in and teach the girl privately.
So my suggestion is for you to not pack your son's bag or suitcase without his involvement. If he has to bring a sleeping bag, have him practice unrolling it and rolling it. If he has a flashlight or battery-operated lantern, make sure he is very familiar with it. He should know what clothes he's bringing and what they're to be used for (clothes for a hike in the woods, a clean shirt to be saved for parents' night, etc). Make sure he is aware of what toiletries and bug spray and sunscreen he has, and how to use them. Have him basically do the packing, with your supervision (so stuff just doesn't get thrown in a scrunched-up bunch into the suitcase).
He'll feel ready, you'll feel secure, and he'll have a wonderful time.